In many areas of importance to Canadians, including environmental monitoring, medical diagnostics, food safety, forensics, and basic biological research, the ability to perform biological and chemical agent detection is of paramount importance. There is a growing need for instruments that perform fast, accurate, and inexpensive sample manipulation and processing with high-throughput. Currently, such large scale analysis is performed using slow conventional lab techniques (e.g. microbial culture at a central laboratory) or large table-top systems. More recently, devices based on microfluidics offer possibilities for: 1) the fast manipulation and sorting of large numbers of samples, and 2) multiplexed analysis of a single sample for many different constituents—utilizing a system that is small enough to be portable or even hand-held.
Microfluidics deals with the precise control of micro- to nano-liters of fluid. The benefits of scaling chemical processes to this level include extremely low volumes of samples and reagents that can be very expensive, highly parallel processes for massive throughput, faster reaction times, and safer testing through decreased volumes of dangerous samples and reactions. Called “lab-on-a-chip” (LOC), these types of systems face a number of key challenges. When scaled to microscale fluidic channels, surface tension, capillary forces, and other fluid dynamics become major considerations. Microfluidics applications usually require external pressure sources through pumps or centrifugal force; or electrokinetics for flow. Liquids must be precisely manipulated, necessitating separate microfluidic channels (or “microfluidic tracks”) for each test, resulting in a large array of permanently configured channels occupying a lot of space and limiting the number of parallel tests. Practical applications require LOCs with a plurality of independently controlled valves to achieve true LOC functionality. Furthermore, the majority of technologies thus-far employed for multiplexed fluid manipulation require large off-chip support devices (e.g., pneumatics), or are based on other technologies (e.g., electrowetting, described below) that offer promise, but have relatively strict requirements for the fluid sample manipulation and sample transfer between devices.
Following the analogy of digital microelectronics, the approach of open structures, where discrete, independently controllable droplets are manipulated on a substrate using binary electrical signals is referred to as “digital microfluidics”. By using discrete unit-volume droplets, a microfluidic operation may be defined as a set of repeated basic operations, i.e., moving one unit of fluid over one unit of distance. Droplets may be formed using surface tension properties of the liquid. Actuation of a droplet is based on the presence of changing the surface tension (or wetting) of the fluid electronically, using electrical forces generated by electrodes placed beneath the bottom surface on which the droplet is located. Different types of electric forces can be used to control the shape and motion of the droplets. One technique that can be used to create the foregoing electric forces is based on the aforementioned electrowetting which relies on the dependence of the contact angle of the droplet on voltage and may utilize DC or low-frequency AC field. Droplets are placed on a surface having electrodes located beneath the surface. The shape and motion of the droplets may be controlled by switching the voltages of the electrodes. By sequentially energizing and de-energizing the electrodes in a controlled manner, one or more droplets can be moved along a path or array formation of electrodes. Detection or analysis related to processing of one or more droplets using the device is performed “on-chip” (that is on the device itself), such as using “on-chip” electrical and/or optical detection. One such technique that may be used is laser induced fluorescence (LIF) in which a droplet is moved to a location on the device and a laser beam is directed onto the droplet causing optical emissions from molecules that have been excited to higher energy levels by absorption of electromagnetic radiation. Emission of fluorescent light therefrom may be used to detect whether a particular reaction occurred. It should be noted that droplets can thus be moved, mixed, and analyzed on-chip.
In contrast to digital microfluidics is technology related to “continuous-flow microfluidics”, which is based on manipulation of liquid flow through micro-fabricated channels. Actuation of liquid flow is implemented either by external pressure sources, external mechanical pumps, integrated mechanical micropumps, capillary forces, electrokinetics, or by combinations of capillary forces and electrokinetic mechanisms. Conventionally known continuous-flow devices are adequate for many well-defined and simple biochemical applications, and for certain tasks such as chemical separation, but they are less suitable for tasks requiring a high degree of flexibility or in effect fluid manipulations. These closed-channel systems are inherently difficult to integrate and scale because the parameters that govern flow field vary along the flow path making the fluid flow at any one location dependent on the properties of the entire system. Permanently etched microstructures also lead to limited reconfigurability and poor fault tolerance capability. Methods that seek to solve the reconfigurability aspects have thus far been based mainly on a type of microfluidic valving that requires a large amount of support equipment to drive arrays of, e.g., pneumatic valves, resulting in a “chip-in-lab” situation rather than a self-contained “lab-on-chip”.
There remains the need for a simple, portable, versatile, easily configurable, continuous-flow device which is adaptable in in-situ and portable testing environments. It is an object of the present invention to obviate or mitigate the above challenges and disadvantages.